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Alternator or voltage regulator

909 Views 28 Replies 7 Participants Last post by  vwnate1
Hi all

Hope you’re all well, w123 200 m115 engine (petrol) manual.

Went for a drive and indicators stoped working lights dim. When I parked up battery light came on and it was dead. Battery was old so put in brand new one (voltage was over 12.6) started up straight away but then the battery light was on constantly.

I checked the voltage and when engine running was giving me over 13.7v, I changed the voltage regulator (from original Bosch 0192052008) to a hella replacement one. Once fitted started all ok but battery readout varies at 12.15v when the car is running even with heater on full and lights on. Battery light is still on in dash though.

So is it a case of dodgy voltage regulator or alternator? Should I check the earth? Also a little bit of oil leak from before and it’s been pretty cold wet in the uk.

Any ideas or steps to check?

Thanks
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1979 w123 200 m115 petrol manual
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Discussion Starter · #3 ·
Welcome to you. Can I recommend putting your car model and year into your profile for us please? Complete your Profile

I don't think I'd trust any other VR than Bosch, personally.
apologies added details, ah I understand what you mean. I couldn’t find any, should I goto Mercedes directly? Anything else I could check to clarify if it is the regulator?
 

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.................... ~'84 300D~~~~~~~~ ~~'85 300TD~~~~~~~ ~~~W123(s) Galore~~~
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You did not state if the headlights or other consumers of electricity were on when you read the 13.7 volts. When testing anything make sure all variables are the same so that you can distinguish differences. If any electrical consumers were on during your first test I would say that 13.7 @ idle is good.

I get 14.2 @ idle... no consumers.
I get 13.6 - 13.8... depending on the number & type of consumables @ idle.

I have a Brand New Bosch Alternator.

CLEAN ALL GROUND CONTACTS!!!
 
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Discussion Starter · #5 ·
You did not state if the headlights or other consumers of electricity were on when you read the 13.7 volts. When testing anything make sure all variables are the same so that you can distinguish differences. If any electrical consumers were on during your first test I would say that 13.7 @ idle is good.

I get 14.2 @ idle... no consumers.
I get 13.6 - 13.8... depending on the number & type of consumables @ idle.

I have a Brand New Bosch Alternator.
Hi
Ah thanks both times no lights/heater etc was on.

will do some more tests and put back the results

thanks for the help
 

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Ground Contacts: Clean where the Battery Cable meets the Fender, there is another from the Starter to the Bell Housing. I would also add a ground wire from the instrument cluster to the Fire Wall... this one is a big deal and probably does more to 'fix' instrument cluster issues than anything else. I'm speaking to mid 80(s) W123 Diesels yours may vary.
If I missed one guys... please chime in.
 
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Discussion Starter · #7 ·
Ground Contacts: Clean where the Battery Cable meets the Fender, there is another from the Starter to the Bell Housing. I would also add a ground wire from the instrument cluster to the Fire Wall... this one is a big deal and probably does more to 'fix' instrument cluster issues than anything else. I'm speaking to mid 80(s) W123 Diesels yours may vary.
If I missed one guys... please chime in.
Okey dokey will have a clean of them, as due to a slight oil leak and bit of rust over the years

thanks
 

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Why would someone only clean the grounds? Clean all of the battery connections.
I am assuming that the alternator on the gasser has the same alternator electrical connector.

Don't know how much room there is to do this on the gasser. When you remove the alternator electrical connector you will see that it can be taken apart.
I suspect what you are going to find is the are the wire connect to the brass connector and or the brass is corroded. Depending on what you find will determine your action.

While the electrical connector is out remove the voltage regulator and look inside at the metal sort of finger that makes contact with the voltage regulator if that is corroded it needs to be cleaned.

This is a pic a corroded contact finger
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Also look inside at the condition of the slip ring.

There is also a test using an electrical multi-meter (volt Ohm meter) that checks for AC current. One of the names for the test is a voltage ripple test.
What it is about is that you can appear to have good charging voltage but there is a diode issue that is putting out too much AC voltage.

Do a google image search and there are various videos on how to do it. Due to the type of plug-in electrical connector you limited to reading it over the 2 battery terminals. The main thing is you need to know what AC voltage to set the meter to.

There is also another test called the voltage bypass test that will tell you if your battery cables have too much resistance. Again, instructions on the internet buy doing a google image search.

I put in a different battery ground to chassis cable and found I got a whole other volt during charging afterwards

If your probe the disconnected alternator electrical connector with your voltmeter:
The 2 large slots on the alternator electrical connector should always have battery voltage. The single smaller slot should have no voltage when the key is off.
On the diesel when you turn the key on the voltage only drops about .3-.5 volts. I am not sure how much the voltage drops on a gasser due to the ignition and if it has an electric fuel pump.
 

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Discussion Starter · #9 ·
Why would someone only clean the grounds? Clean all of the battery connections.
I am assuming that the alternator on the gasser has the same alternator electrical connector.

Don't know how much room there is to do this on the gasser. When you remove the alternator electrical connector you will see that it can be taken apart.
I suspect what you are going to find is the are the wire connect to the brass connector and or the brass is corroded. Depending on what you find will determine your action.

While the electrical connector is out remove the voltage regulator and look inside at the metal sort of finger that makes contact with the voltage regulator if that is corroded it needs to be cleaned.

This is a pic a corroded contact finger
View attachment 2801419

Also look inside at the condition of the slip ring.

There is also a test using an electrical multi-meter (volt Ohm meter) that checks for AC current. One of the names for the test is a voltage ripple test.
What it is about is that you can appear to have good charging voltage but there is a diode issue that is putting out too much AC voltage.

Do a google image search and there are various videos on how to do it. Due to the type of plug-in electrical connector you limited to reading it over the 2 battery terminals. The main thing is you need to know what AC voltage to set the meter to.

There is also another test called the voltage bypass test that will tell you if your battery cables have too much resistance. Again, instructions on the internet buy doing a google image search.

I put in a different battery ground to chassis cable and found I got a whole other volt during charging afterwards

If your probe the disconnected alternator electrical connector with your voltmeter:
The 2 large slots on the alternator electrical connector should always have battery voltage. The single smaller slot should have no voltage when the key is off.
On the diesel when you turn the key on the voltage only drops about .3-.5 volts. I am not sure how much the voltage drops on a gasser due to the ignition and if it has an electric fuel pump.
Cool! Ok mate will get cracking with the suggestions, thanks so much. Appreciated, will update with results on these.
 

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Good write-up 300D. The primary grounds are frequently a common issue and an obvious quick check point... as pointed out by the 1 volt gain when installing a new ground cable ...as, previously mentioned. Yes... absolutely, ohm test and can clean every single contact point throughout the entire vehicle as time allows. I've probably done this a few of times on each vehicle over the years. o_O
 
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Discussion Starter · #11 ·
Ok
Due to time/weather etc could only do voltage test so far
12.4 before start
12.08 when running (even at high revs)
11.56 when lights hazards and heater on full
12.4 when I tuned the engine off

I cleaned the ground contacts and the inside of the alternator clip. I tried both voltage regulators (original Bosch) and the hella replacement results were the same.

Will do the other tests in the next day or so (subject to weather)
 

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Keep at it!!!

If you have a trickle charger you may want to keep that new battery fresh while you are not working on the car as you are draining the battery... even @ idle. It will not be long before you will start getting 12.2 and then 12.1 etc 'before start' unless the battery gets some charge.

I hate to say it... but, I smell a 'new alternator' in the not to distant future.
 

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Discussion Starter · #13 ·
Keep at it!!!

If you have a trickle charger you may want to keep that new battery fresh while you are not working on the car as you are draining the battery... even @ idle. It will not be long before you will start getting 12.2 and then 12.1 etc 'before start' unless the battery gets some charge.

I hate to say it... but, I smell a 'new alternator' in the not to distant future.
Yeh I will do… ill keep an eye on it.
Thinking the same… down the route of a refurb or new one?
 

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Rebuilds are fine... they are around 200 (including a core charge) so you will get 50 or 60 back ... so, 140 to 150 range (with free shipping).
Shop around and get it from someone reliable like Pelican, ECS Tuning etc. Don't trust eBay Sellers.

OH! Get the 65amp Rebuild! Double OH! Sorry, Yer a BRIT! Still don't get it off eBay!
 

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Discussion Starter · #16 ·
Rebuilds are fine... they are around 200 (including a core charge) so you will get 50 or 60 back ... so, 140 to 150 range (with free shipping).
Shop around and get it from someone reliable like Pelican, ECS Tuning etc. Don't trust eBay Sellers.

OH! Get the 65amp Rebuild! Double OH! Sorry, Yer a BRIT! Still don't get it off eBay!
Cool will do, most eBay ones available for uk are from Germany. But will have a hunt around while I’m waiting to do other tests.
Cheers mate
 

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Cool will do, most eBay ones available for uk are from Germany. But will have a hunt around while I’m waiting to do other tests.
Cheers mate
You can get alternators rebuilt at small places that do these and starter motors. Can be a great way of avoiding cheap shite parts.
 

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In the US you can remove the alternator itself and get that tested for free. When you do that, it bypasses all of your wiring and switches and lets you know if here is an issue inside of the alternator.
I think you are at that point where having the alternator tested off of the vehicle is desirable.

There is another area that can have a bad ground. And that is the bottom where the alternator pivots. They are usually badly rusted.

Some people have run another ground wire to the alternator housing itself. But of course, you need a good contact there meaning bare metal.

The alternator housing in the picture is kind of corroded. One end of the voltage regulator has to make clean bare metal contact with the alternator housing.
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my 123 coupe ran on its optima battery until it was completely discharged as the alternator failed. a rebuilt one was obtained thru o'reilly, I believe it took two days to arrive as we were not in a heavily populated area of AZ. I had no warning that the alternator was not charging the battery, there was no warning light on the dash nor was there an amp meter in the dash cluster. The rebuilt alternator worked fine and a 2 amp battery charger/tender brought the battery back to 12.4V after five days. Optima batteries require low amperage charges, a standard battery charger which puts out 6 or more amps can kill an optima battery.
 
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